Re: 2D Elastic Collisions

[Bob Sciamanda <trebor@VELOCITY.NET>]

Dan,
        Nature would be rather dull if all elastic collisions with the
same initial kinematical conditions were identical in outcome..  The
general conservation laws (momentum and energy) do not specify the
DETAILS OF THE INTERACTION.  Remember that they only relate the initial
and final conditions - the possible intervening interactions (electric,
magnetic, springs, explosives, ?, etc) are endless in variety.

Given the details of the forces of interaction (eg., Rutherford
scattering) all is determined.

Even a pool table and two billiard balls should provide ample examples
for experimentation (that's why it's a fun game!).

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor
-----Original Message-----
From: Dan Burns <kilroi@LGHS.NET>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Tuesday, November 10, 1998 7:13 PM
Subject: 2D Elastic Collisions


>    I have a student who is bothered by the fact that in a 2D collision
> involving 2 masses (one at rest) there are seven variables (2 masses,
three
> speeds, and 2 directions) and only three equations (x momentum, y
momentum,
> and energy). This means that even if the three initial conditions are
> known, only three of the final four conditions can be determined. This
> implies that there are multiple possible outcomes for a specific
> experiment. He wants to perform experiments to learn about this puzzle.
Can
> anyone shed light on this problem. Our Halliday, Resnick and Walker text
> just says that one of the final conditions must be known.
>
> Dan Burns
> Los Gatos High School